Carbon Quantum Dots–Europium(III) Energy Transfer Architecture Embedded in Electrospun Nanofibrous Membranes for Fingerprint Security and Document Counterspy

Traditional fingerprints are usually obtained by pressing an inked finger on a paper. The inks would contaminate fingers and more importantly, these fingerprints are visible and able to be photocopied. In order to develop a smart membrane for fingerprint recording and document security, microrod assemblies of carbon quantum dots (CQDs)-Eu (III) are embedded in a electrospun nanofibrous (NFs) membrane which has strong red emission under UV irradiation owing to aggregation induced Dexter energy transfer from CQDs to Eu (III) ions. A clear blue emission fingerprint could be recorded on the membrane after a finger touch because the phosphate (Pi) secreted through sweat glands blocks the solid-state Dexter energy transfer, recovering the UV-irradiated blue emissions of CQDs. The Pi-based fingerprint on the membrane, which is invisible under daylight and could not be photocopied, greatly improves the security of the fingerprint and, furthermore, has the capability to identify the people who touched the secret document through the fingerprint analysis, showing that the intelligent NFs membrane can be applied for both fingerprint security and document counterspy.